1. Field of the Invention
The present invention relates to a display system that has a display element having pixels, a tone of each of which is adjustable.
2. Description of Related Art
A conventional display system is known to have a transmissive display element and a backlight. The transmissive display element allows light to transmit therethrough and has pixels, a tone of each of which is adjustable. Also, the backlight provides light toward the display element from the rear side of the display element to thereby backlight the display element. A visible luminance of a screen of the above display system is determined by luminance of the backlight and a tone of the display element. JP-A-H11-194736 (corresponding to U.S. Pat. No. 6,597,338) and JP-A-2008-158497 describe liquid crystal display systems that provide a desired visible luminance by adjusting both of the luminance of the backlight and the tone of the display element.
Sometimes, a part of multiple information sets displayed on the display system is required to be emphasized by displaying the emphasis part with luminance higher than luminance, with which the other information is displayed. For example, the vehicular display system displays (a) normal information sets indicating a current operational state and (b) alert information sets indicating abnormal conditions or urgent conditions. Typically, the alert information sets are indicated by characters or patterns. In order to notify the user of the abnormal conditions or the urgent conditions, the display of the alert information sets is emphasized. For example, the normal information is associated with a vehicle speed and an engine rotational speed, and the alert information is associated with an overheat state. The alert information is displayed on one segment of the display system, and the one segment or pixels for displaying the alert information are displayed with high luminance for emphasizing the information.
Also, in the display system, the visibility of the information is adjusted based on the preference of the user or brightness of extraneous light. More specifically, the visible luminance on the display system is required to be adjusted based on the luminance determined by the user. When the above luminance adjustment is performed, the above emphasized display of the emphasis part is required to be also sufficiently achieved while the luminance is effectively adjusted.
For example, as described in a system of JP-A-2008-158497, a changeable range of the luminance determined by the user is divided into multiple modes, and the luminance of the backlight and the tone of the display element are adjusted for each of the modes. However, the system of JP-A-2008-158497 has a complicated display control disadvantageously.